#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

int abb(int a[], int n)
{
	int num = 0;
	for (int i = 0; i < n; i++)
	{
		num ^= a[i];
	}
	return num;
}

int main()
{
	int b[] = { 1,2,3,4,5,4,3,2,1 };
	int sz = sizeof(b) / sizeof(b[0]);
	int ret = abb(b, sz);
	printf("%d\n", ret);
}